It lasts as long as you're willing to stand in the cold. There is no schedule or agenda. Typically people slowly arrive while a few start building the all important fire. Gifts are exchanged before the light is totally gone (and a handy fire nearby to dispose of the wrapping). Treats are passed around, peple cook stuff over the fire, music is playing, and a lot of chatting. Depending on the temperature, it could be an hour, three hours, half hour, whatever you want it to be. The only gotcha is if you show up late and everyone left because it was too cold. Then there was that one time where the coordinates were wrong..